Torque converter runout

In any converter shop I've been in, converters being welded together and having the runout check are always mounted on a thick steel backing plate. This guaranteed they were square in the lathe. They are bolted to this plate via the mounting nuts or studs on the converter.
Run out is very limited.
You live in Ontario, I'd phone Pat at SMR transmissions, he's in Bradford, and the number there is 888-846-6603, and see what he allows for maximum runout on the converters they build. The shop I worked at is closed now, so I can't call them to give you their specs